Multichannel filtering for wide-band direction finding

A preprocessing stage for wide-band direction finding is formulated in the framework of multichannel filtering wherein the filter frequency response matrices are chosen to achieve signal-subspace focusing. Direction finding based on any narrow-band algorithm is then performed on the filter output. A procedure for specifying a sparse response suitable in nonstationary environments is presented. An approach to filter design that avoids explicit evaluation of the frequency response is proposed. Extensions to beam-space processing are discussed from the standpoint of simple implementation structures. Simulation studies confirm the usefulness of the various focusing multichannel filters